Piranha fossil is 3 feet long

Megapiranha is 3 feet (1 meter) long - 3 times larger than today's modern piranhas. This animal lived 8 to 10 million years ago

A close relative of piranhas, called pacu, is not scary. Pacu has teeth used to chew plants. (Note that the stories that piranhas eat humans are completely fictional.)

The newly discovered jaw bone fossil of a transitional species, called Megapiranha paranensis, has connected the evolutionary gap between carnivorous piranhas and their plant-eating relatives.

These are known:

Today piranhas have a row of triangular teeth, like the blades of a saw, the researchers explain. Pacu has two rows of square teeth, supposedly to chew fruits and seeds.

Wasila Dahdul, scientist at the National Center for Evolutionary Synthesis, North Carolina, said: 'In modern piranhas, teeth are arranged in a row. But in piranha's cousins, usually plant-eating fish, teeth are arranged in two rows'.

Illustration of Megapiranha paranensis, a 3-foot ancestor of modern piranhas. (Photo: Ray Troll)

The new fossil shows a central arrangement: teeth are arranged in a zigzag line. This shows that the two rows of pacu teeth are pressed to form a row in piranha. John Lundberg, curator of the Academy of Natural Sciences in Philadelphia and co-author of the study, said: 'It is like the teeth from the second row' migrate 'into the first row.'

If this is true, Megapiranha may be a transitional step in the long process of forming piranha's special teeth. To understand the location of the Megapiranha in the evolutionary plants of these fish, Dahdul examined hundreds of specimens of modern piranhas and their relatives.

Dahdul said: 'The interesting thing about this group of fish is that their teeth have unique characteristics. Only one tooth can tell you a lot about a fish as well as its other relatives'. The species system analysis confirmed her intuition - Megapiranha seems to lie between piranha and pacu in the evolutionary tree.

Megapirnha fossils were collected at a cliff of the northeastern Argentine river in the early 1900s , but have not been studied until the anthropologist Alberto Cione of the Argentine Museum of La Palta rediscovered a startling specimen - row of upper teeth with 3 large and pointed teeth - in a museum drawer in the 1980s

The picture of the teeth and the fossil jaw of Megapiranha paranensis shows the arrangement of teeth between a single piranha and their two relatives. The fossil is 3 inches long, and the fish is 3 feet long. (Photo: Mark Sabaj-Pérez)

Although no one knows what Megapiranha eats, this animal may have a varied diet.

However, there are still some confusing things. Dahdul said: 'Piranha has 6 teeth, while Megapiranha has 7 teeth. So what happened to the 7th tooth? '

Lundberg explained: 'One of the teeth may have been lost. Or two of the 7 teeth have merged together in evolution. That is a question that has no answer yet. Maybe one day we will discover '.

Piranhas only live in South American freshwater areas, including the Amazon living area. The stories of this animal's violent attack on humans are completely fictional.

According to Encarta Encyclopedia and other sources: 'There are no human deaths from being attacked by piranhas. They often eat worms and small fish. One of their habits is to eat a small part of the fin or scales of other fish. This allows prey to survive and regrow damaged parts, providing a renewable food source for piranhas'.